1. Field of the Invention
This invention relates to an optical switch matrix which selects propagation route between I/O parts by electric control.
2. Description of the Prior Art
The optical switch matrix has switch elements at each crosspoint of the matrix, which change direction of an optical signal.
In order to propagate optical signals efficiently, it is important that propagation loss in passing switch elements is reduced.
A switch element employed for a conventional optical switch matrix is illustrated in FIG. 1.
In FIG. 1, a switch element is composed of directional coupler 60 and waveguide 63a, 63b, 64a, 64b. The directional coupler 60 has two parallel waveguides 61 and 62. Electrodes 65 and 66 are formed respectively on the parallel waveguie 61 and 62. The parallel waveguide 65 is jointed between waveguide 63b and 64a. The parallel waveguide 66 is jointed between waveguide 63a and 64b. Corner reflectors 67-70 are formed at their joint corners.
For example, in FIG. 1, an optical signal imputed into waveguide 63a reflects on the corner reflector 69, and propagates in parallel waveguide 62. As a result of interaction between parallel waveguide 61 and 62, the optical signal is transfered to the parallel waveguide 61. Then, the optical signal reflects on the corner reflector 68, and propagates in the waveguide 63b.
On the other hand, by controling voltage applied to the electrodes 65 and 66, the optical signal is not transfered from the parllel waveguide 62 to the parallel waveguide 61. In this case, the optical signal reflects on the corner reflector 70, and then propagates in the waveguide 64b.
However, in passing each switch element, the optical signal reflects on the corner reflectors two times necessarily. As to m X n matrix for example, the optical signal may reflect on corner reflectors maximum (m+n-1).times.2 times propagation paths. Propagation loss occurs every time the optical signal reflects.